1. Field of the Invention
The invention relates to compositions of polymeric materials comprising polyamides; more particularly the present invention relates to compositions comprising two polyamides wherein the composition features improved crystallization rates. The invention also relates to methods for forming such compositions of polymeric materials.
2. Description of the Prior Art
As is well known to the art, thermoplastic polymeric materials which feature a high degree of crystallinity in the final formed article are highly desirable. Such highly crystalline polymeric materials exhibit improvements in several key properties, including resistance to mold shrinkage, heat distortion temperature, maximum dimensional stability and resistance to deformation, hardness, abrasion resistance, tensile yield strength and surface hardness.
To induce or to improve the rate of crystalline formation of a polymer from its amorphous state, typically its molten state which exists during the processing of the polymer and prior to its final molding, casting or shaping step, it is known in the art to use a variety of nucleating agents or other crystalline promoters. Examples of such crystalline promoters include those described in Nylon Plastics, M.I. Kohen, J. Wiley & Sons, New York (1973), at p. 424.
For polyamides, known crystallization promoters include finely divided particulates such as those described in U.S. Pat. No. 3,549,651 to Oswald et al. wherein the use of finely divided agents selected from a select group used in conjunction with a plasticizing agent are used in minor amounts relative to the quantity of the polyamide. Other crystallization promoting additives include the system described in U.S. Pat. No. 4,749,736 to Khanna et al. wherein are discussed polyamide compositions which comprise nucleating agents including finely divided inorganic materials, one or more low molecular weight polymers, and one or more fatty acid amides. Further crystallization promoters known to the art include those described in U.S. Pat. No. 3,645,932 wherein are disclosed a group of nucleating agents selected from: polymers and copolymers of monoolefins having of 2-6 carbon atoms the ionomer of ethyleneacrylic acid copolymer, a polyamide of .epsilon.-caprolactam, a polyamide of .omega.-amino undecanoic acid, a polyamide of .omega.-aminododecanoic acid, a polyamide of hexamethylene diamine and adipic acid, a polyamide of hexamethylene diamine and sebasic acid, or a copolyamide resin derived from polymeric fatty acids, sebasic acid and bis-amino-ethylbenzene, polycarbonate of p,p-1 -isopropyliodenediacrylonitrile, butadiene and styrene, natural rubber, balata and paraffin wax, which are dispersed in the polymeric material.
While these nucleation promoters provide beneficial improvements to the compositions within which they may be incorporated, there remains a continuing need in the art to provide molding compositions and nucleation promoters for molding compositions which feature improved characteristics.